I. Field of the Invention
The present invention relates to polyurethanes and poly(ureaurethanes) prepared from branched polyols, branched polyisocyanates and/or polyisocyanate trimers, articles and coatings prepared therefrom, and methods of making the same.
II. Technical Considerations
A number of organic polymeric materials, for example plastics such as polycarbonates and acrylics, have been developed as alternatives and replacements for glass in applications such as optical lenses, fiber optics, windows and automotive, nautical and aviation transparencies. For example, in aircraft glazings both polycarbonates, such as LEXAN®, and acrylics have enjoyed widespread acceptance. These polymeric materials can provide advantages relative to glass, including shatter or penetration resistance, lighter weight for a given application, flexibility, ease of molding and dyeability. Unfortunately, there are some serious disadvantages associated with both polycarbonates and acrylics. Polycarbonates scratch easily, and if directly exposed to sunlight and harsh environments soon become difficult to view through. Acrylics, although not as scratchable as polycarbonates, do not have the physical properties of the polycarbonates such as heat distortion temperature and impact resistance. Some “high impact” strength polycarbonates can have inconsistent impact strength that can degrade over time, poor crack propagation resistance (K-factor), poor optical quality, poor solvent resistance and poor weatherability. Even though polycarbonates can exhibit good impact strength when impacted at low speeds, at high impact speeds of greater than about 1100 ft/sec (335.3 m/sec), such as those exhibited in ballistics applications, a 9 mm bullet (125 grain) fired from about 20 feet (6.1 m) at a speed of about 1350 ft/sec (411 m/sec) can pass easily through a 1 inch (2.5 cm) thick polycarbonate plastic.
Also, polycarbonates are typically extruded, which can produce optical distortions in the extrudate in the direction of extrusion. For optical applications such as fighter plane canopies, polycarbonates typically must undergo an additional processing step to remove the distortions, which can increase cost. Also, some polycarbonates are birefringent which can also cause optical distortions. For example, the Abbe number of LEXAN is 34. Higher Abbe values indicate better visual acuity and less chromatic aberrations.
Thus, there is a need in the art to develop polymers useful for producing articles having good optical quality, high impact resistance, high impact strength, high K factor, good ballistics resistance, good solvent resistance and good weatherability. The ability to fabricate articles by casting or reaction injection molding rather than extrusion also is desirable.